Cut the onion into small (1/4-inch) dice. Seed the bell pepper, if using,
and cut into small dice. Rinse the tofu and pat it dry, then cut it into
medium (1/2-inch) dice.
Heat the oil in a wok or large skillet over medium-high heat. Once the oil
shimmers, add the onion and pepper, if using; stir-fry for 1 to 2 minutes,
until fragrant and softened a bit.
Add the tofu; stir-fry for 1 minute, then add the corn, mustard, ketchup,
barbecue sauce and Sriracha (to taste); stir-fry for about 5 minutes or
until the mixure is heated through and evenly blended.